The present invention relates to a sample tube rack assembly for holding, positioning and transporting sample tubes in an automated sample handling system.
Automated sample handling systems are known which automatically dispense patient fluid samples, such as blood plasma, along with reagents and other additives, into the reaction well of a cuvette which is then automatically positioned for monitoring or performing tests on the fluid sample. For example, in U.S. application Ser. No. 07/833,950, now U.S. Pat. No. 5,236,666, to Hulette et al, entitled "Temperature Regulation in a Sample Handling System for an Optical Monitoring System", there is disclosed an automated sample handling system for an optical evaluation instrument that can handle a high throughput of patient samples with a high degree of versatility, adaptability and reliability. The invention according to Hulette et al allows for walk-away automation for a sample handling system, once sample tubes containing patient samples are loaded into the system.
Accurate positioning and stabilizing of the sample tube within an automated system is essential. For example, in the aforementioned system disclosed by Hulette et al, a sample tube is advanced to a piercer where a piercing probe is caused to pierce the septum of the sample tube. A sample probe is lowered a predetermined distance into the sample tube to aspirate a programmed amount of sample. The sample probe is then removed from the sample tube and the sample subsequently dispensed into a cuvette.
However, sample tubes are manufactured in various brands and sizes having diverse parameters. For example, sample tubes manufactured by Beckton Dickinson of Rutherford, N.J. and sold under the brand name of Vacutainer with Hemogard Closure typically have a length of 75 mm and a diameter of 13 mm. In contrast, sample tubes made by Sarstedt and sold under the brand name of Monovette Microtainer can have a length of 65 mm and a diameter of 12 mm. Further, sample tubes may have different sizes depending on their particularly designed purpose. For example, the Monovette Microtainer brand sample tubes can have a length ranging from 65 mm to 92 mm. Consequently, the aforementioned automated systems typically are limited to using one standard size of sample tube for all tests and procedures to be run or by requiring that all of the sample tubes of a particular transport rack be of the same size. However, this latter option requires that expensive sensors and software be used to signal to the system the type of sample tubes contained within the rack so that the system "knows" when the sample tube has been pierced. Further, sample tube racks typically have several receptacles for holding several corresponding sample tubes. Requiring that all sample tubes of a particular rack be of the same size may result in empty receptacles within a rack being transported through the system, thereby decreasing the overall efficiency and flexibility of the system.